The disclosures herein relate generally to a human patellar implant and more particularly to an apparatus and method of preparing a patella for implanting a patellar prothesis.
Preparation of a human patella for implanting a patellar prothesis is a multi-step process involving the removal of bone material and requires the use of several surgical tools. The need for such a prothesis is usually for correcting arthritic damage to the patella. Ideally, the same amount of bone removed from the patella is replaced by the prothesis so that the reconstructed patella will replicate the natural patella.
Generally, the surgical steps of such a procedure include preparation of the patella, reaming the patella, and securing the implant to the reamed patella. The reaming procedure is generally accomplished by securing the patella in a clamp and reaming a cylindrical bore in a portion of the patella to allow for insertion of an implant therein. The implant is then press-fit into the bore, or pressed into the bore and held in place by a clamp until a bonding agent cures to secure the implant in the patella.
Various tools and procedures have been developed to accomplish the above. U.S. Pat. No. 5,180,384 discloses a method for preparing a patella for receiving a patellar implant and for implanting a prothesis therein. An elongated passageway is formed in the patella which is then reamed to form a cavity of a size and configuration to receive the patellar prothesis using a cannulated reamer telescoped over a guide rod positioned in the elongated passageway.
In U.S. Pat. No. 5,284,482, a universal patellar clamp is disclosed. The clamp includes an articular surface clamping member having a central aperture defining a centerline axis. The central aperture is sized to accept all available known sizes of cannulated reamers. An anterior clamping member is positioned along the centerline axis and is movable with respect to the articular clamping member to effect clamping of the patella. A pair of guide arms are engaged with the articular clamping member to be positioned over the central aperture and provide a guide hole for supporting a threaded guidewire or pin along the centerline axis. The guide arms are removable from their position over the central aperture to clear the aperture for access by the cannulated reamer.
U.S. Pat. No. 5,520,692 discloses an adjustable depth patella recessing guide and method for guiding a cutting tool to recess the posterior surface of a patella. The guide includes a body having a first end for engaging the posterior surface of the patella, having a second end, and having a bore extending between the first and second ends for allowing the cutting tool to pass therethrough. A depth gauge is mounted within the bore of the body for movement in a direction between the first and second ends of the body. The depth gauge includes a stop for stopping the cutting tool. A lock mechanism is provided for locking the depth gauge to the body.
In U.S. Pat. 5,536,271, a system is disclosed for preparing a natural patella for implantation of a patellar prothesis. Substantially the same amount of bone removed from the natural patella is replaced by the prothesis so that the reconstructed patella will replicate the natural one in diameter and thickness. To this end, the patella is held stationary and two operations are performed simultaneously. First, a posterior side of the patella is resected to form a prothesis receiving surface for reception of a fixation surface of the patellar prothesis. Second, a mounting bore is formed into the resected surface of the patella for reception of fixation members of the patellar prothesis. A reamer is guided for movement between a first position spaced from the posterior surface of the patella, and a second position in operative engagement with the patella, at which formation of both the receiving surface and of the mounting bore therein has been completed. The reamer is stopped at the second position which is preselected according to the thickness of the patella, such that the amount of the patella removed is substantially equal to the thickness of the patellar prothesis.
U.S. Pat. No. 5,575,793 discloses an improved patella clamp apparatus including a scissor-like instrument fame having a pair of handles at one end portion. A patella holder and drill collet have gripping surfaces for holding a patient's patella therebetween during preparation for implantation of a prothesis. The collet has arcuate slots for accepting the vertical ridge of the patella. A reamer or cutting instrument cuts a circular recess into the posterior face of the patella. The collet is supported by the frame and positioned opposite the elevator. The collet accepts a depth stop for referencing the posterior aspect of the patella. The collet provides a bore that supports a reamer or drill for forming the circular recess in the patella posterior surface.
In U.S. Pat. No. 5,658,291, a median ridge referencing system and method of use in prosthetic knee implantation surgery is provided. The median ridge referencing system comprises a patella clamp including a guide sleeve having a length and a lumen extending through the length and referencing device comprising a stop ring and stop plug. The ring may be coupled to the guide sleeve at a plurality of locations along the length of the guide sleeve. The stop plug is removably coupled to the stop ring, and extends into the lumen of the guide sleeve until it reaches the bone. The stop ring is then coupled to the guide sleeve and the stop plug is removed. A reamer is inserted into the lumen of the guide sleeve and used to ream the patella until the reamer's stop reaches the top of the stop ring. When the reamer reaches the top of the stop ring, the patella has been reamed to the proper depth for insertion of the patella prosthesis.
In U.S. Pat. No. 5,716,360, a patella recession instrument and method provides a guide for producing an oval, tri-oval, or elliptically shaped recess on the posterior surface of the osteotomized patella for receiving a similarly shaped backing portion of a patellar implant. The apparatus includes a guide bushing and a bushing positioning mechanism for securing the bushing against the posterior of the osteotomized patella, with a guide opening formed through the bushing covering the total area to be recessed. A reamer guide structure, which may be a separate structure received in the bushing guide opening, or integrally formed with the bushing, receives one or more rotary reamer tools in a plurality of reaming positions. The cutting face of the rotary reamer tool in each different reaming position covers a different portion of the total area to be recessed. The recession method includes securing the guide bushing in the proper operating position against the patella, sequentially positioning the cutting face of the reamer tool or tools in the plurality of different reaming positions, and operating the tool or tools to produce a series of intermediate recesses that combine or approximate the total area to be recessed.
U.S. Pat. No. 5,716,362 discloses a patella milling instrument having a planar base with a fixed patellar clamping element formed thereon. A movable patellar milling element is slidably mounted on the base and is movable towards and away from the fixed clamping element. A drive element is operable between the base and the movable element for moving the movable clamping element. The drive element is actuated by a drive mechanism fixed in a handle of the device found at one end thereof and connected to a drive element which is also in the form of a ratchet element. A movable end mill type cutting element is mounted on a support arm supported by the base. The support arm is capable of movement in directions parallel to the plane of the base and is adjustable in a direction perpendicular to the base. The end mill has a drive shaft rotatably mounted in a bushing in an end of the support arm. The drive shaft is rotatable by a power tool and capable of movement in a direction perpendicular to the plane of the base.
Other attempts have been made to produce an efficient, easy-to-use patella reaming system for establishing the proper bore depth. However, these systems have commonly relied on the use of cumbersome spacers, commonly referred to as "donuts", to set the depth of penetration that a reamer makes when forming the bore for the insert. Still, other systems have used cumbersome external scales, calipers, threaded stop-nuts, fixed stops, or other devices to achieve this purpose. Each of these systems requires numerous, time consuming steps for making tool and attachment changes.
Therefore, what is needed is an apparatus and a method which permits the surgeon to predicably control reamer penetration depth, make one handed adjustments if needed, and made quick reamer size exchanges during the procedure.